Hydrochemical Characterization and Organic Pollution Assessment of an Urban River Catchment under Anthropogenic Pressure: The Case of the Téguéré River (Korhogo, Côte d'Ivoire)

Abstract

Rapid and unplanned urbanisation in Sub-Saharan African cities exerts severe pressure on urban aquatic ecosystems due to the lack of adequate sanitation systems. This study evaluates the hydrochemical quality and organic pollution levels of surface water in the Téguéré River catchment (Korhogo, northern Côte d’Ivoire) to assess its suitability for human consumption and agricultural irrigation. Physical and biochemical parameters were analysed across ten sampling points from upstream to downstream. Hydrochemical facies were identified using Piper diagrams, while organic biodegradability and irrigation suitability were determined via COD/BOD₅ ratios and the Sodium Adsorption Ratio (SAR), respectively. The results show high turbidity (up to 322 NTU) and critical concentrations of NH4+ (0.2–2.09 mg/L), total Fe (0.3–12.08 mg/L), and Mn2+ (0.19–8.05 mg/L), all exceeding WHO drinking water guidelines. COD (6.9–52 mg/L) and BOD5 (3.2–24.4 mg/L) levels, paired with a constant COD/BOD ratio of 2.1, demonstrate a moderately biodegradable organic load of domestic origin. Three dominant hydrochemical facies were classified: Ca-Mg-HCO3 (80%), Ca-Cl (10%), and Na-K-Cl (10%). Crucially, while unfit for drinking, the water remains suitable for irrigation, plotting within the low-to-medium salinity and low sodium hazard zones (C1S1 and C2S1 classes) with a SAR < 1. Water quality significantly deteriorates downstream due to untreated urban runoff and water treatment plant effluents. The immediate implementation of tailored filtration systems and continuous monitoring is urgently required to safeguard public health and local ecosystems.